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Bba_C0051 cI-Lamba, the promoter in disguise
During the construction of one of our larger pieces of the spatial oscillator, the ON switch, we stumbled upon an unexpected phenotype.
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Our scanned image of our plate with colonies containing RBS-C0051 ligated to RBS-RFP. Click above for the full-screen image.
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- Our intermediate ligation of RBS-C0051 to RBS-RFP produced a red phenotype but it has no promoter!
- Since Bba_C0051 is a highly studied and widely used part in the registry, it presents a huge problem not only in the context of the spatial oscillator but also in the 76 parts that utilize it throughout the registry.
- This exciting new find causes many problems in our design and must cause malfunctions in a huge number of parts entered and used in the registry.
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- We began by sequencing the DNA of the red colonies from the ligation of RBS-C0051 to RBS-RFP in order to rule out the presence of any promoter or mutation. The sequence analysis revealed that we did indeed have the correct sequence. Results of our C0051 w/ LVA tag sequence..
- Further investigation into Bba_C0051 showed that the part not only contained the coding region, cI, but it is also followed by an LVA degradation tag and a barcode. When looking further into the RBS (Bba_E1010), we found that it also contained an LVA degradation tag and a barcode after the RFP coding region.
- We then conducted a number of experiments in order to determine which part or combination of parts contained in the construct caused this unwanted promoter-like behavior.
- After determining the cause of the unwanted transcription, we continued to conduct a number of experiments in order to measure the results.
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Our scanned image of our plate with colonies containing RBS-RFP. No abnormalities here! Click to enlarge.
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- The previous step in the construction of the on switch was RBS-RFP.
- This construct clearly exhibited a white phenotype. No abnormalities here!
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- To determine whether Bba_C0051 played a role in the unexpected transcription, we ligated RBS-RFP to RBS-RFP in order to see if transcription occurred.
- The construct exhibited a white phenotype. Thus, we concluded that transcription did not start in any part of the RFP. This helped to narrow our focus down to the possibility of the cI coding region in Bba_C0051 or a possible artifact in the plasmid as the cause for the unwanted transcription.
- After the results were in, we diligently sent them out for sequencing so that we would be sure that our results were accurately reflecting the parts that we believed we were analyzing.
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Our scanned image of our plate with colonies with C0051 into Chris Anderson's promoter screening plasmid. Click to enlarge.
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- Next, we sought to determine whether the presence of an artifact in the plasmid might be the cause or contribute to the promoter function.
- We ligated RBS-C0051 to Chris Anderson's Promoter Screening Plasmid (Bba_J23006)
- By changing the context in which the parts were placed, we were able to removing the possibility of the artifact causing transcription
- Even after placing this part into a new context, we obtained red colonies! Therefore, we know that the transcription initiation has something to do with the Bba_C0051 region.
- Sequenced? Yes!
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Our scanned image of our plate with colonies containing RBS-RFP in Chris Anderson's PSP. Click above for the full-screen image.
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- Now, although the presence of an artifact from the original plasmid has been determined to be negligible, it is also important to verify the same for Chris Anderson's Promoter Screening Plasmid (Bba_J23006)
- We ligated RBS-RFP into Chris Anderson's Promoter Screening Plasmid (Bba_J23006)
- A white phenotype was expressed. Therefore, it is clear that we must focus down on the Bba_C0051 part in order to determine where a promoter function is being expressed.
- Once again, of course this part was sequenced!
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- To determine where in Bba_C0051 transcription is initiating, we decided to perform a 5' RACE PCR on Bba_C0051
- The experimental data is shown below:
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Data to be inserted
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- As shown, the transcription that we are seeing clearly starts at the beginning of the barcode region
- So, what does this all mean?
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Modified C0051 in PSP exhibited white phenotype. Click above for the full-screen image.
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- From all the test so far, it is clear that a certain interaction of the cI coding region and the barcode are acting together to produce some kind of promoter function.
- In order to experimentally provide data to prove this point, we removed the barcode from the RBS-C0051 construct and placed it into Chris Anderson's Promoter Screening Plasmid (Bba_J23006).
- Surely enough, the phenotype was white!
- We finally narrowed it down and were able to create a part in which the cI lambda coding region can be utilized without creating an unwanted and detrimental promoter function.
- This part was sequenced and submitted!
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- By removing the barcode and submitting this part to the registry, we have greatly improved a fundamental part by modifying it so that it works as advertised.
- As you can imagine, an unwanted constant transcription can really set you back and cause major malfunctions in your system.
- With this necessary fix implemented, you can now feel confident that this fundamental part will work just as you intend!
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- We are currently working to clearly pinpoint the place in the cI-lambda coding region that interacts with the barcode and caused transcription.
- In order to achieve this, we have designed primers, which are used to carefully truncate Bba_C0051. After these truncations are made, we will observe their phenotype in order to determine our results.
- Also, we are in the process of characterizing and measuring the relative strength of the promoter present in the system containing a barcode.
- We look forward to sharing the results of these quantitative tests at the iGEM Jamboree ‘10.
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We would like to take a moment to thank all of our sponsors for their very generous donations, as we could not have done this without your help!
We would also like to thank and acknowledge:
Our Advisors
Marc Facciotti
Ilias Tagkopoulos
Technical Guidance
David Larsen
Andrew Yao
Visiting iGEMer
Jia Li of Zhejiang University (TEAM ZJU-China)
cI Promoter Screen
Drew Endy - Stanford
Thomas Schneider - NIH
Want to sponsor us? Send an email to mtfacciotti@ucdavis.edu to discuss various ways you can help! :)
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